Silver thick film pastes for low temperature co-fired ceramics: impact of glass frit variation Jayashri Bangali Thick Film Materials & Electronics Packaging Division, Centre for Materials for Electronics Technology, Pune, India and Department of Electronic Science, University of Pune, Pune, India Sunit Rane and Girish Phatak Thick Film Materials & Electronics Packaging Division, Centre for Materials for Electronics Technology, Pune, India, and Shashikala Gangal Department of Electronic Science, University of Pune, Pune, India Abstract Purpose – The purpose of this paper is to investigate and report the impact of glass frit variation in silver thick film pastes used as surface conductors in low temperature co-fired ceramics technology (LTCC), especially on the properties such as warpage of LTCC associated with conductors, microstructure of the fired thick films, sheet resistance and adhesion on LTCC. Design/methodology/approach – Silver thick film paste compositions were formulated by changing the silver glass frit ratio. The compatibility of these formulated paste compositions with LTCC (DP 951AX) substrate were evaluated. The properties such as microstructure developments, the change in sheet resistance, warpage of LTCC substrate with respect to glass frit ratio of the developed silver films on LTCC were evaluated. Findings – The results reveal that the glass frit percentage used in paste formulation is equally responsible for the disturbance in the properties such as microstructure, warping and electrical properties of the fired thick films on LTCC. It was observed that the paste composition, in particular sample SP10B containing the highest glass frit percentage, is compatible with the LTCC tape under processing conditions. The sheet resistance value in the range of 5 mV/A and the fired films showed very good adhesion (3.95 N), irrespective of the glass frit composition. Originality/value – The paper provides useful evaluations of properties such as microstructure developments, changes in sheet resistance and warpage of LTCC substrate with respect to glass frit ratio of the developed silver pastes on LTCC. Keywords Silver, Surface conductivity, Films (states of matter), Adhesion, Sheets, Pastes Paper type Research paper Introduction The rapidly growing wireless industry requires advanced, high-performance materials to build low loss, high density and thermally stable integrated packages for applications such as automotive, safety, control, global positioning system, mapping and entertainment, mobiles, video and data transmission through wireless local area network, etc. Recently, low temperature co-fired ceramics (LTCC) technology has been referred to as a key approach for smart packaging. LTCC is a new integrated packaging technology from a combination of thick film and LTCC, is an essential part of system-in-package technology, where electronic systems are based on modules. This technology is compact, the products are light and it offers high speed with higher interconnect density for portable wireless communication systems (Jagtap et al., 2008). The LTCC modules are often fabricated using noble metals such as gold, silver and copper because of compatibility of these metals with LTCC systems and because they offer superior electrical conductivity. Gold finds major use in aerospace and high-reliability applications due to its stability and oxidation resistance, but it is also highly expensive. On the other hand, silver is much lower in cost and can be fired in air, making it very attractive for more cost sensitive markets. However, silver tends to suffer from electromigration and therefore has not been widely adopted in high-reliability applications. However, effective encapsulation of the silver in the ceramic can circumvent the impact of electromigration (Barlow et al., 2007). In addition to the cost, the advantage of silver over other conductors is that it has the lowest electrical resistance; it is thermodynamically stable below 2008C in the oxide form and above 2008C it deoxidises to metallic silver (Imanaka, 2005). Copper is also inexpensive but because of its strong affinity for oxygen, special inert firing atmospheres are required. However, no extensive research reports are available on the development of conductor compositions compatible to LTCC. Regardless of the metal selected, the thick film inks used in LTCC systems are not identical to those used on conventional alumina. These thick film compositions must be tailored to be chemically compatible with the tape dielectrics during the sintering process and must offer the correct viscosity for the intended application. The material systems are offered with a range of inks for different applications such as internal connections or via fill. Via fill inks are generally more viscous than inks intended for printing interconnects. The current issue and full text archive of this journal is available at www.emeraldinsight.com/0954-0911.htm Soldering & Surface Mount Technology 20/3 (2008) 41–46 q Emerald Group Publishing Limited [ISSN 0954-0911] [DOI 10.1108/09540910810885714] The authors are grateful to Messrs Vivek and Shrikant for their kind help in sample firing and warpage measurement and Mrs Vijaya for Scanning Electron Microscopy. 41